Most modern RV water heaters (WH) operate in either Electric or Liquid Propane (LP) Gas mode.
In entry level RVs though, the water heater may only operate in LP gas mode.
Water heaters in other motorhomes might operate by a third heating method called Motoraid (see more below), which uses waste heat from the motorhome engine to heat the water as you drive.
Finally, some high end RVs may have an entirely different system in which the water heater is part of a diesel and electric central heating system, typically either the Aquahot or Hydrohot brand names.
These systems are an entirely different animal and will not be discussed here.
Standard RV Water Heater Basics
The standard RV water heater sizes are 6 gallon or 10 gallon – much smaller than residential heater.
If you’re new to RVing, you may find that you’re not be able to enjoy quite as long a hot shower as at home. A few models are advertised as being 16 gallon heaters, but these are actually 10 gallon heaters that superheat the water and then mix cold water at the outlet, making them roughly equivalent to having a 16 gallon heater at the usual 140 degrees.
There will be separate On/Off switches for the Electric and LP Gas Modes. The RV water heater can be operated in either mode or both can be used to speed up the heating process.
Both are controlled by a thermostat, so the heater only runs as needed.
In LP gas mode, a heater control circuit board insures safe operation, so 12v power is needed for it to operate.
Most water heaters have separate thermostats for Electric and LP Gas modes and the two modes are pretty much independent of each other.
If one doesn’t work for some reason, usually the other will still be functional.
The standard thermostats are fixed temperature, typically 140 degrees in recent models, and you can’t adjust them.
However, there may be adjustable replacement thermostats available for some brands & models.
RV Water Heater: Electric Mode
An RV water heater in Electric Mode can be used whenever you have 120v shore or generator power available.
It requires a fairly substantial amount of electricity, about 12 amps (1400 watts), so you may not want to utilize it if power is limited, or if you want to run other high power appliances (like an air conditioner or microwave oven) at the same time.
This is primarily a concern in RVs that have only 30A shore power wiring, or anytime the RV is plugged into an outlet that has 30A or less available.
You can switch it off temporarily (the water will stay hot for some time) or change over to LP Gas mode.
When you switch on the Electric mode on your RV water heater, the Electric Mode thermostat controls whether 120v power flows to the electric heater element or not.
The heater element cycles on & off as needed, heating the water, just like your home water heater. There is no need to turn the heater off when not in use.